2007 Cobalt LT -- have cleared P0128 several times in the last few months, finally took the advice shown here on another post and replaced the thermostat. Mine looked like the one in the other post photo with the inner gasket/seat torn up. It was the original one, car has about 72k miles. No leaks, seems to work ok. Engine runs cool -- between 180 deg F and 195 most of the time. Replaced the coolant sensor too since I bought one earlier thinking it had failed to cause the "---" reading on the instrument panel.